Telephone repeater circuit arrangement



July 14, 1931-. J. URMSTON ET AL I 1,814,775

TELEPHONE? REPEATER CIRCUIT ARRANGEMENT Filed Feb. 11, 1930 h 0 going.circuit, respectively.

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Patented July 14, 1931 um'rso STATES [PATENT OFFICE 'rELErnoEE RErEA'rEn cmcurr .AnaianeEfiEnr Application fi led Februar 11, 1930, Serial No. 427,592, and in .ereat Britain February 15, 1929.

Those portions of telephone circuits in which repeating devices are inserted are, as is well-known, only effective for currents flow ing in one direction since the amplifying ac- 5 tion of the repeater is only applied to cur rents flowing in one direction. Accordingly,

- for such telephone lines, two circuits are necessarwhich, when considered from one end, may e called the incoming and the .out-

For combined two-way working it is'a. practical necessity to couple these two circuits together at each end.- At this coupling, there is the incoming and the outgoing circuits and the joint circuit 15 which may, for instance, be the local? circuit in which thetelephone instrument is inserted. By this coupling, it is provided that two-way workin from the joint circuit may take place, t at is to say, currents originating in ,20 the"local circuit may flow out and pass lnto the outgoing circuit, and currents arriving by the incoming circuit may pass to the local circuit. There is, however, unless precautions I are taken to prevent'it, the possibility that 2 currents arriving by the incoming circuit may pass in part into the outgoing circuit and re-circulate' through the line, producing the effect of echoes. The present invention provides an im roved arrangement for bringing about this inter-connection of the incgming circuit, the outgoing circuit, and the localcircuit, without permitting the recirculation of an appreciable proportion of the incoming currents.

It will be seen to it, currentsgoing from the local circuit or from the incoming circuit; the former must be allowed to pass'as freely'as possible, while taining this result isthe use of an-arrangement of a double inductive coupling between the incoming and outgoing circuits so formed that the two. part-s'of the coupling produce e filects which oppose, each other in the o'utgomg circuit when they are energized by currents which arrive at the junction by way of the incoming circuit. By application Sesecond link between the incoming and outeflective in that circuit;- -By appropriate dethat at the point of inter cohnection, the outgoing circuit may have applied the latter must be restricted as much as possi-' ble. One of the methods proposed for atr1111 No. 361,624 filed 9th May 1929 an im proved arrangement of this kind has been described. In that arrangement the two transformers by which the two inductive couplings between the incoming and outgoing circuits are brought about are the junction transformer by which the outgoing and local circuits are coupled with the incoming circuit and a second transformer called the coupling transformer which establishes a going circuits. Each of these transformers has a' winding in the incoming circuit and a winding which is either placed directly in the outgoing circuit or is otherwise caused to be sign-of the transformers and their associated circuits it is provided that when current is arriving at the junction byway of the incoming circuit the eflects of'the two windings on the outgoing circuit are substantially equal and opposite and therefore produce no appreciable resultant; On the othervhand the arrangement providesthat the coupling transformer leaves unaffected or assists the effect in the outgoing circuit of currents which arrive at the junction by way of the local circuit. This difi'erentiation between the action of currents on the outgoing circuit in accordance with the path by which they reach the junction is obtained by the difference of'phase relation of the currents in the incoming and outoing circuits in the two cases which results rom'theform of coupling between the threecircuits made by th junction transformer.

The present inv ntion is an improvement 5, in or modification of the subject matter of the above mentioned applications;

In accordance with this invention the second inductive coupling is connected with the incoming circuit at a point in that circuit, .33, where a thermionic valve is interposed between the connection and the junction. One of the results of this arrangement isthat' currents coming to thejunction by way of the local circuit, cannot penetrate to an appreci- I53 a'ble extent through the incoming circuit to the coupling circuit.

' Since this arrangement'will in general provide that amplification of the incoming current takes" place between the connection to 2:3

' with the grid and filament connections of the valve in the incoming circuit and connecting the anode and filament of this valve 1n series with a winding of the coupling transformer,

an appropriate battery being also included.

The invention will be further described by the aid of the accompanying drawing which shows diagrammatically the application of the invention to a circuit arrangement as shown by Figure 3 of the drawings of the application previously referred to. From'this example the application of the invention to other arrangements, for instance that of F igure 4 of the previous case, will be readily recognized. The incoming circuit 1 is coupled with the outgoing circuit 2-and the local circuit 3 by'the transformer having the wind- I ings 4, 5 and 6,.that is the junction transformer. The other inductive coupling is effected by way of the transformer having the windings 8, 17- and 9. The winding 8 being associated with the incoming circuit, the winding 9 with the outgoing circuit and the wind-- ing 17 with an artificial balancing network 18. The windings 9 and 5 are connected in series in the grid filament circuit of the valve 10 and are so connected as to oppose each other when energized by currents coming to the junction by way of the incoming circuit.

In accordance with the present invention thewinding 8 is connected with the incoming circuit at a point where the valve 15' is interposed between the. connection and the junction and a second valve 20 is arranged as part pf the circuit of the winding 8. This valve has its filament and grid connected in parallel with the filament and grid respective ly of 'thevalve 15. The winding 8 is in the filament-anode circuit of this valve 20;

With this arrangement currents arriving by way of theincoming circuit willinfluence equally the grids of both valves 15 and 20 and accordinglywill give rise to similar effects inthe windings 4: and 8 whichfwill be communicated to-the windings 5 and 9-s0 as to be substantially equal and opposite therein. -This arrangement provides for the second inductive coupling without placing any additional load on the valve 15 so that the whole of the output of this valve energizes the junction transformer and passes thereby to the local circuit instead of being divided between this circuitoand the balancing network 18 as is the case where the coupling trans former is connected with the incoming circuit t a point between the'valve 15 and the juncti and two-wire circuits.

The new arrangement will also modify the conditions which exist when the currents arrive at the junction by way of the local circuit since the one-way connection between the anode filament and grid filament circuits of the amplified valve 20 is now present and ods of adjustment may be used in combination. The grid voltage adjustment maybe obtained by utilizing a tapped transformer or choke coil or resistance placed across the incoming circuit. This matching of characteristics of valves is required since it is important that the characteristics of the two circuits, by which the incoming and outgoing circuits are bonnectedtogether, should resemble each other as closely as possible.'

The elements of the two valves 15 and 20 may conveniently be combined together in a single structure preferably having a single filament and one or two grids and two anodes, the two arrangements being electrically symmetrical so as to give matched characteristics.

The invention is applicable in the same way as the arrangements described in the earlier applications mentioned to four-wire What We claim as our sire to secure by Letters Patent is 1. A'telepho'ne repeater circuit arrangement comprising an incoming circuit, an outgoing circuit, a local circuit, two inductive coupling devices between the incoming andoutgoin .circuits, opposing each other in their e ects in the outgoing circuit when energized by currents which arrive at thejunction through the incoming circuit; one

invention and deof ,saidcoupling devices being the junction transformer by which the outgoing and the local circuits are conpled with the incoming circuit and the other of said devices being the coupling transformer, for coupling the incoming and the outgoing circuits; an amplifier arrangement, said amplifier arrangement comprising two similar amplifiers one of which is inserted in the incoming circuit and feeds the junction transformer and the other of which is connected on its input side in parallel with the input of the first amplifier and on its output side is connected with a winding of the coupling transformer.

2.-A telephone repeater circuit arra g ment comprising an incoming circuit, an outgoing circuit, a. local circuit, two induc-* tive coupling devices between the incoming and Outgoing circuits, opposing'each other in their effects in the outgoing circuit when energized by currents which arrive at the junction through the incoming circuit; ,one of said coupling devices being the junction transformer by which the outgoing and the local circuits are coupled with the incoming circuit and the other of said devices being the coupling transformer which couples the incoming and the outgoing circuits and comprises a winding connected to a balancing network; and an amplifier arrangement comprising two similar amplifiers one of which is inserted in the incoming circuit and feeds the junction transformer and the other of which is connected on its input side in paral- 0 lel with the input of the first amplifier and on its output side is connected with a winding of the coupling transformer.

3. A telephone repeater circuit arrangement comprising an incoming circuit, an outgoing circuit, a local circuit, two inductive coupling devices between the incoming and outgoing circuits, opposing each other 1 in their effects in the outgoing circuit when energized by currents which arrive at the unction through theincoming circuit and an amplifier arrangement, one of said coupling devices beingthe junction transformer comprising a winding in the outgoing circuit, a winding in the incoming circuit and a wind-- ing in the local circuit and the other said device being the coupling transformer comprising a winding in the outgoing circuit, a winding connected with the amplifier arrangement and a winding connected with a' 4 balancing network; the amplifier arrangement comprising two similar amplifiers one of which is inserted in the incoming circuit and feeds the junction transformer and the other of which is connected on its input side in parallel with the input of the first I amplifier and, on its output side is connected with the before mentioned winding on the coupling transformer.

In testimony whereof we havehereunt'o set our hands.

JAMES URMSTON. FREDERICK STRETTON SMITH. 

